Fix reading beyond end of bignum in integer squaring

The multiplication of two bignums is specially optimized when the two
operands have the same address, because squaring can be done more
efficiently than multiplication of two arbitrary integers.  That is,
expressions such as `I * I` will be calculated by squaring the value
of `I`.

The optimized function for squaring would read one word beyond the
end of the bignum in the last iteration of a loop. The garbage
value would never be used. In almost all circumstances that would
be harmless. Only if the read word happened to fall on the start
of an unmapped page would the runtime crash. That is unlikely
to happen because most bignums are stored on a process heap, and
since the stack is located at the other end of the block that the
heap is located in, the word beyond the end of bignum is guaranteed
to be readable.

0 files changed, 0 insertions, 0 deletions